The invention relates to a plasma picture screen provided with a phosphor layer. The invention further relates to a luminous screen provided with a phosphor layer, a phosphor preparation, and a phosphor.
Plasma picture screens render possible color pictures of high resolution and large picture screen diagonal, and they have a compact construction. A plasma picture screen comprises a hermetically closed glass cell which is filled with a gas, with electrodes arranged in a grid. The application of a voltage causes a gas discharge which generates light in the ultraviolet range. This light can be converted into visible light by means of phosphors and can then be emitted through the front plate of the glass cell to the viewer.
It is important for achieving a sufficient picture contrast in daylight that the plasma picture screen should have a high luminance in combination with a reflection of external light which is as low as possible. The characteristic quantity for this property is the so-called Luminance Contrast Performance (LCP):   LCP  =            Luminance      ⁢              xe2x80x83            ⁢              (        L        )                            Reflection        ⁢                  xe2x80x83                ⁢                  (          R          )                    
The contrast may be improved, and accordingly also the LCP value, for example, in that the phosphors are pigmented with inorganic pigments. The inorganic pigments are chosen such that they are as transparent as possible to the color emitted by the respective phosphor while absorbing the remaining spectral components.
JP 11-131059 describes a phosphor for plasma picture screens which is pigmented with an inorganic pigment in the same manner as the phosphors for cathode ray tubes. Since the VUV radiation used for exciting phosphors in plasma picture screens has only a small penetration depth into the phosphor particle, a pigmentation of the phosphor particle will clearly reduce its efficiency.
It is accordingly an object of the present invention to avoid the disadvantages of the prior art and to provide an improved plasma picture screen.
This object is achieved by means of a plasma picture screen provided with a phosphor layer which comprises a phosphor which is intrinsically pigmented.
It is advantageous here that the pigmentation of the phosphor is not achieved externally through the application of inorganic pigments on the surface of the phosphor particles, but that the phosphor is pigmented on the inside. It is avoided thereby that the efficiency of the phosphor is reduced in that the VUV light is absorbed by the pigments provided on the surface.
It is particularly advantageous that the phosphor is intrinsically pigmented in that the host lattice of the phosphor comprises an ion which has absorption bands within the host lattice in the wavelength range of the emission of the phosphor.
Owing to this advantageous embodiment of the pigmentation, the phosphor is given an intrinsic color which corresponds to its emission color. Since the intrinsic color of the phosphor corresponds to its emission color, the phosphor shows a high reflection at its emission color, whereas the remaining spectral components are less strongly reflected. It is prevented thereby that the reflected daylight mixes itself with the colored light emitted by the phosphor and thus weakens the contrast.
It is particularly advantageous that the phosphor has the composition (Ba1xe2x88x92xxe2x88x92ySrx)(Mg1xe2x88x92zCoz)oAlpOq:Euy with 0xe2x89xa6X less than 1, 0.01xe2x89xa6Yxe2x89xa60.40, 0 less than z less than 1, o=chosen from the groups 1 and 3, p=chosen from the groups 10 and 14, and q=chosen from the groups 17 and 23.
These intrinsically pigmented phosphors efficiently convert VUV radiation into colored light.
The invention further relates to a luminous screen provided with a phosphor layer and to a phosphor preparation, each comprising a phosphor which is intrinsically pigmented.
Intrinsically pigmented phosphors may be used to particular advantage in luminous screens of optical display devices in which the exciting radiation cannot penetrate pigment particles, with which a similar intrinsic color of the phosphor is achieved, without appreciable energy loss.
The invention further relates to a phosphor with the composition (Ba1xe2x88x92xxe2x88x92ySrx)(Mg1xe2x88x92zCoz)oAlpOq:Euy with 0xe2x89xa6x less than 1, 0.01xe2x89xa6yxe2x89xa60.40, 0 less than z less than 1, o=chosen from the groups 1 and 3, p=chosen from the groups 10 and 14, and q=chosen from the groups 17 and 23.